The present invention relates to a bleed valve for tapping or bleeding a portion of the inlet air for a gas turbine engine, more particularly such a valve that is self regulating and which provides minimal disturbances in the air flow duct.
It is well-known in the art to tap or bleed a portion of the inlet air for a gas turbine engine to provide a pressure differential on opposite sides of bearing seals to preclude oil leaks, to cool or heat components of the turbojet engine in order to control operational clearances, or to provide air conditioning or warm air to an aircraft cabin.
As a rule, the air is tapped or bled at the gas turbine engine compressor and may be tapped between the low pressure compressor and the high pressure compressor, or from the cold air flow when the turbojet engine is the turbo fan type. The selection of the source of the bleed air depends upon the desired temperatures and pressures of the air.
Usually the air bleeding or tapping is carried out in an air flow of which the speed and pressure vary dramatically according to the operational mode of the gas turbine engine, or as a function of altitude or speed in the case of an aircraft turbojet engine.
The known bleed valves frequently suffer from the drawbacks of unnecessarily high cost and unnecessarily high weight, and may tap an excessive amount of air from the duct, especially under high power engine operation. Accordingly, the engine compressor must be oversized to ensure an adequate supply of air to the engine thereby increasing its cost and weight and lowering the efficiency of the compressor. Frequently, the excessive air tapping or bleeding deteriorates the efficiency of the elements to which the tapped air is supplied and may, for instance, increase oil consumption at the oil trap.
French Patent No. 2,257,787 discloses an air tapping device for use on a gas turbine engine compressor which comprises a butterfly valve located in the air flow conduit which is controlled by a piston subjected on one side to the upstream air pressure and on the other side to a spring biasing device and atmospheric pressure through a second valve. The piston and the valve shaft are linked by a link rod and a crank. This patent also discloses an air tapping device comprising a valve also designed as a piston subjected to the upstream pressure, the atmospheric pressure and a spring return force.
French Patent No. 2,680,832 discloses a device for tapping air from a gas turbine engine comprising an articulating and retractable conduit which, in its active position, intercepts a portion of the gas flow along a duct wall. This device also includes control means located outside of the conduit.